1. Field of the Invention
The present invention pertains to flexible polyurethane foam compositions and methods for the preparation thereof. More particularly, the present invention relates to high resilience, open-celled, flexible polyurethane foam compositions characterized by fine uniform cell structure and little or no shrinkage or foam collapse.
2. Description of the Prior Art
Polyurethane foams are formed by reacting a polyisocyanate with a polyol which may be a polyether containing hydroxyl groups or a polyester containing hydroxyl groups in the presence of a blowing agent, a catalyst and a surfactant. The blowing agent may be CO.sub.2 generated by a water isocyanate reaction. Other blowing agents include methylene chloride and fluorocarbons whereby heat generated when the polyisocyanate reacts with the polyol evaporates the blowing agent so it passes through the liquid mixture forming bubbles therein. If a surfactant is not used in the foaming composition of a high resiliency flexible foam, the bubbles simply pass through the liquid mixture without forming a foam.
In the past, many surfactants were used to form a foam from the liquid mixture, as well as to control the size of the bubbles of the foam so that a foam of a desired structure was obtained. Preferably, a foam with small bubbles or cells therein of uniform size is desired in that it has the most desirable physical properties such as tensile strength, elongation and tear as well as improved comfort characteristics. Also, it is desirable to have a foam with open cells which does not collapse prior to forming a strong gel or curing. In the past, it was discovered that polysiloxanes having oxyalkylene units in the polymer chain were useful as surfactants in foaming polyurethane. However, these polysiloxanes are expensive and a need has been developed for an inexpensive substitute for these conventional commercially-available silicone surfactants which are commonly used as cell stabilizers in high resiliency molded flexible urethane foams. Accordingly, in accordance with the prior art, a dimethylsiloxane has been used alone in various formulations and particularly those which contain graft polyol and tin catalyst. This has been found to give desirable fine open cells at the surface of the foam where it contacts the mold, however, insufficient stability within the interior of the foam can result in foam collapse. The addition of very small amounts of highly efficient polysiloxane-polyoxyalkylene surfactants along with dimethylsiloxane stabilize the cells so effectively that they do not open when the foaming reaction is complete and shrinkage occurs.
Accordingly, it is the purpose of the instant invention to provide high resiliency, molded, open celled flexible polyurethane foam compositions characterized by small bubbles or cells of fine uniform size which are open and do not collapse prior to forming a strong gel on curing.
______________________________________ References U.S. Pat. No. Issued Inventor Assignee ______________________________________ 4,139,503 2/13/79 Kollmeier et al Th. Goldschmidt AG 3,669,913 6/13/72 Morehouse Union Carbide 3,920,587 11/18/75 Watkinson Union Carbide 4,163,830 8/7/79 Windemuth et al Bayer 3,050,477 8/21/62 Gmitter et al General Tire 4,147,847 4/3/79 Schweiger Dow Corning 4,081,410 3/28/78 Moeller General Electric ______________________________________
U.S. Pat. No. 4,139,503 is directed to a process for production of high resilience open-celled polyurethane foams which do not shrink in storage wherein from 0.01 to 2.0 grams per 100 grams of polyol of specific siloxane components are added to the foaming charge. The siloxane components are selected from the group consisting of straight-chain or branched organopolysiloxanes and polyoxyalkylene-polysiloxane block copolymers. An example of the polysiloxanes which may be employed is polydimethyl siloxane.
U.S. Pat. No. 3,669,913 discloses a solution composition particularly useful for the manufacture of flexible polyether urethane foam which includes a hydrolytically stable siloxane-oxyalkylene block copolymer along with a water-soluble silicon-free organic surfactant. Suitable organic surfactants include ethylene oxide adducts of nonylphenol which contain as high as 20 ethylene oxide groups. This patent also discloses that polyether polyols suitable for the production of polyurethane foams are graft polymer polyether compositions obtained by polymerizing ethylenically unsaturated monomers in a polyether.
U.S. Pat. No. 3,920,587 discloses a process for production of open-cell rigid polyether polyurethane foam employing as the cell opening agent a siloxane-oxyalkylene block copolymer. This patent also discloses the inclusion as other conventional additives, diol foaming modifiers, for example, ethylene glycol, polyethylene glycol and the like.
U.S. Pat. No. 4,163,830 discloses the use of polysiloxane-polyoxyalkylene copolymers as stabilizers in the production of polyurethane foam plastics. Further, the patent states that the relatively high viscosity of the stabilizers used in accordance with the invention is often a disadvantage. Accordingly, the end products of the process are preferably used in solution in solvents and preferred solvents are polyethers which can contain as high as 100 oxyethylene groups. Further, the example shows a stabilizer which has its viscosity reduced simply by mixing the stabilizer with a 1,3-propylene glycol initiated polyether, in which propylene oxide and ethylene oxide in a mixing ratio of 50:50 have been polyadded in the presence of catalytic quantities of sodium alcoholate.
U.S. Pat. No. 3,050,477 relates to a method of making polyurethane foam using an organic silane stabilizer which may use a diol modifier to improve the foaming action. Among the listed examples of such modifiers are polyethylene glycol with an average molecular weight of 1000 and polyethylene glycol with an average molecular wight of 1500.
U.S. Pat. Nos. 4,147,847 and 4,081,410 both disclose siloxane-oxyalkylene copolymers as foam stabilizers in flexible foams.